1. Field of the Invention
This invention relates generally to the determination of various downhole parameters in a subsurface formation penetrated by a wellbore. More particularly, this invention relates to the determination downhole parameters, such as annular, formation and/or pore pressure, during a drilling operation.
2. Description of the Related Art
Present day oil well operation and production involves continuous monitoring of various subsurface formation parameters. One aspect of standard formation evaluation is concerned with the parameters of reservoir pressure and the permeability of the reservoir rock formation. Continuous monitoring of parameters such as reservoir pressure and permeability indicate the formation pressure change over a period of time, and is essential to predict the production capacity and lifetime of a subsurface formation.
Present day operations typically obtain these parameters through wireline logging via a “formation tester” tool. This type of measurement requires a supplemental “trip” downhole. In other words, the drill string must be removed from the wellbore so that a formation tester may be run into the wellbore to acquire the formation data and, after retrieving the formation tester, running the drill string back into the wellbore for further drilling. Thus, it is typical for formation parameters, including pressure, to be monitored with wireline formation testing tools, such as those tools described in U.S. Pat. Nos.: 3,934,468; 4,860,581; 4,893,505; 4,936,139; and 5,622,223. Each of these patents is limited in that the formation testing tools described therein are only capable of acquiring formation data as long as the wireline tools are disposed in the wellbore and in physical contact with the formation zone of interest. Since “tripping the well” to use such formation testers consumes significant amounts of expensive rig time, it is typically done under circumstances where the formation data is absolutely needed, when tripping of the drill string is done for a drill bit change or for other reasons.
The availability of reservoir formation data on a “real time” basis during well drilling activities is a valuable asset. Real time formation pressure obtained while drilling will allow a drilling engineer or driller to make decisions concerning changes in drilling mud weight and composition, as well as penetration parameters, at a much earlier time to thus promote the safety aspects of drilling. The availability of real time reservoir formation data is also desirable to enable precision control of drill bit weight in relation to formation pressure changes and changes in permeability so that the drilling operation can be carried out at its maximum efficiency.
Techniques have been developed to acquire formation data from a subsurface zone of interest while the downhole drilling tool is present within the wellbore, and without having to trip the well to run formation testers downhole to identify these parameters. Examples of techniques involving measurement of various downhole parameters during drilling are set forth in U.K. Patent Application GB 2,333,308 assigned to Baker Hughes Incorporated, U.S. Pat. No. 6,026,915 assigned to Halliburton Energy Services, Inc. and U.S. Pat. Nos. 6,230,557 and 6,164,126 assigned to the assignee of the present invention.
Despite the advances in obtaining downhole formation parameters, there remains a need to further develop reliable techniques which permit data collection during the drilling process. Benefits may also be achieved by utilizing the wellbore environment and the existing operation of the drilling tool to facilitate measurements. It is desirable that such techniques be provided that are automatic and/or without the need of signals from the surface to activate operation. It is further desirable that such techniques provide one or more of the following, among others, simplified operation, minimal impact on the drilling operation, fast operation, minimal test volume, external testing of a variety of downhole parameters, elimination of test flow line, multiple test devices about the tool for multiple opportunities for test results, reduction or elimination the use of motors, pumps and/or valves, low power consumption, reduction in moving parts, compact design, durability for even high impact operations, rapid response. Added benefit would be achieved where such a device could be used in combination with a pre-test piston to provide pressure readings, pretest functions as well as other downhole data.